1,721,180 research outputs found
Economic conditions predict prevalence of West Nile virus.
Get PDFUnderstanding the conditions underlying the proliferation of infectious diseases is crucial for mitigating future outbreaks. Since its arrival in North America in 1999, West Nile virus (WNV) has led to population-wide declines of bird species, morbidity and mortality of humans, and expenditures of millions of dollars on treatment and control. To understand the environmental conditions that best explain and predict WNV prevalence, we employed recently developed spatial modeling techniques in a recognized WNV hotspot, Orange County, California. Our models explained 85-95% of the variation of WNV prevalence in mosquito vectors, and WNV presence in secondary human hosts. Prevalence in both vectors and humans was best explained by economic variables, specifically per capita income, and by anthropogenic characteristics of the environment, particularly human population and neglected swimming pool density. While previous studies have shown associations between anthropogenic change and pathogen presence, results show that poorer economic conditions may act as a direct surrogate for environmental characteristics related to WNV prevalence. Low-income areas may be associated with higher prevalence for a number of reasons, including variations in property upkeep, microhabitat conditions conducive to viral amplification in both vectors and hosts, host community composition, and human behavioral responses related to differences in education or political participation. Results emphasize the importance and utility of including economic variables in mapping spatial risk assessments of disease
Pathogen-mediated evolution of immunogenetic variation in plains zebra (Equus quagga) of southern Africa
Get PDFIn this thesis, I examined the evolution of two equine Major Histocompatibility Complex (MHC) genes, DRA and DQA, over the history of the genus Equus and across free-ranging plains zebra (E. quagga) populations of southern Africa: Etosha National Park (ENP), Namibia and Kruger National Park (KNP), South Africa. Furthermore, I evaluated the relationships between the DRA locus and parasite intensity in E. quagga of ENP, to elucidate the mechanisms by which parasites have shaped diversity at the MHC. In equids, the full extent of diversity and selection on the MHC in wild populations is unknown. Therefore, in this study, I molecularly characterized MHC diversity and selection across equid species to shed light on its mode of evolution in Equus and to identify specific sites under positive selection. Both the DRA and DQA exhibited a high degree of polymorphism and more intriguingly, greater allelic diversity was observed at the DRA than has previously been shown in any other vertebrate taxon. Global selection analyses of both loci indicated that the majority of codon sites are under purifying selection which may be explained by functional constraints on the protein. However, maximum likelihood based codon models of selection, allowing for heterogeneity in selection across codons, suggested that selective pressures varied across sites. Furthermore, at the DQA locus, all sites predicted to be under positive selection were antigen binding sites, implying that a few selected amino acid residues may play a significant role in equid immune function. Observations of trans-species polymorphisms and elevated genetic diversity were concordant with the hypothesis that balancing selection is acting on these genes. Over the past half century, the role of neutral versus selective processes in shaping genetic diversity has been at the center of an ongoing dialogue among evolutionary biologists. To determine the relative influence of demography versus selection on the DRA and DQA loci, I contrasted diversity patterns of neutral and MHC data across the E. quagga populations of ENP and KNP. Neutrality tests, along with observations of elevated diversity and low differentiation across populations relative to nuclear intron data, provided further evidence for balancing selection at these loci among E. quagga populations. However, at the DRA locus, differentiation was comparable to results at microsatellite loci. Furthermore, zebra in ENP exhibited reduced levels of diversity relative to KNP due to a highly skewed allele frequency distribution that could not be explained by demography. These findings were indicative of spatially heterogeneous selection and suggested directional selection and local adaptation at the DRA locus. There still remains a great deal of discussion over the mechanisms by which pathogens preserve immune gene diversity. The leading hypotheses that have been predominantly considered are: (i) heterozygote advantage (i.e. overdominant selection), (ii) rare allele advantage (i.e. frequency-dependent selection), and (iii) spatiotemporally fluctuating selection. An increasing number of studies have investigated MHC-parasite relationships to reconcile this debate, with conflicting results. To elucidate the mechanism driving the population-level patterns of diversity at the DRA locus, I examined relationships between this locus and both gastrointestinal (GI) and ectoparasite intensity in plains zebra of ENP. I discovered antagonistic pleiotropic effects of particular DRA alleles, with rare alleles predicting increased GI parasitism and common alleles associated with higher tick burdens. These results supported a frequency-dependent process and because maladaptive 'susceptibility alleles' were found at reduced frequencies, suggested that GI parasites exert strong selective pressure at this locus. Furthermore, heterozygote advantage also played a role in decreasing GI parasite burden, but only when a common allele was paired with a more divergent allele, implying that frequency-dependent and overdominant selection are acting in synchrony. These results indicated that an immunogenetic tradeoff may modulate resistance/susceptibility to parasites in this system, such that with MHC-based resistance to GI parasitism, a fitness cost is incurred to the host in the form of increased ectoparasite susceptibility. It is also suggested that these selective mechanisms are not mutually exclusive. (Abstract shortened by UMI.
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The ecology of anthrax and coinfection trade-offs from an immunological perspective: seasonal aspects of host susceptibility
Get PDFSeasonal fluctuations in infectious disease incidence are common, and have been observed for many infectious agents. Immune condition can also change seasonally due to such pathogen fluctuations, a well as to changes in other stress-inducing and immunomodulatory factors such as reproduction and lactation. In addition, most vertebrate hosts are concurrently infected with multiple pathogens, and such coinfections can interact with each other, with the immune system, and with other physiological factors to affect both the individual hosts and population dynamics. While many studies regarding the effects of coinfections and immune trade-offs have been conducted in laboratory settings, similar studies in wildlife are as yet very rare. Fewer studies have been conducted regarding disease and immune seasonality, as these are difficult to model in laboratory settings and require difficult, longitudinal studies in natural systems. In addition, most research regarding disease seasonality in natural systems that has been done has focused on the impacts of abiotic factors on pathogen and vector survival and abundance, or on population-wide dynamics, rather than on physiological mechanisms of host susceptibility. To fully understand the ecology of infectious diseases and the reasons for disease outbreaks, it is necessary to extend laboratory studies into natural hosts in natural systems, as well as to extend wildlife studies to incorporate the complex interactions between environmental, physiological, and coinfection factors. My dissertation research thus focused on the ecological immunology of infectious disease in a natural system, from physiological, seasonal, and coinfection perspectives. I examined the ability of plains zebra (Equus quagga), springbok (Antidocas marsupialis), and African elephant (Loxodonta africana) to respond immunologically to regular anthrax outbreaks in an endemic anthrax system (Etosha National Park, ENP, Namibia). I also examined how zebra and springbok macroparasite coinfections varied with and affected changes in immune parameters, stress, reproductive hormone levels, and seasonal timing of anthrax outbreaks. Despite the fact that anthrax is an ancient disease known to affect wildlife, livestock, and humans on nearly every continent, its natural ecology is not well understood. In particular, little is known about the adaptive immune responses of wild herbivore hosts against Bacillus anthracis, the causative agent of anthrax. Thus, I worked to determine the extent to which natural anthrax hosts can fight off sublethal anthrax doses via adaptive immunity. I used enzyme-linked immunosorbent assays, and developed new assay mensuration rules to determine serum antibody titers against the anthrax protective antigen (PA) toxin, an important, potentially protective aspect of adaptive immunity against anthrax. I found that more than 60% of all zebra, up to 15% of springbok, and up to 50% of elephants had measurable anti-PA antibody titers, indicating that these hosts experience and survive sublethal anthrax infections, likely encounter more anthrax in the wet season compared to in the dry, and can partially booster their immunity to B. anthracis over time. Most pathogen-pathogen interactions occur indirectly through the host immune system, and are particularly strong in mixed micro-macroparasite infections because of the strong immunomodulatory effects of helminth parasites. As pathogen transmission changes with season, host immunity may be more strongly influenced by coinfection immunomodulatory effects than by external factors such as changing dietary and demographic patterns. I thus examined the seasonality of immune functionality, pathogen infectivity, and interactions between concurrent infections and immunity in wild zebra in ENP, a system with strongly seasonal patterns of gastrointestinal (GI) helminth infection intensity and concurrent anthrax outbreaks. I found evidence that wet seasons in ENP are characterized by Th2-type immune skewing driven by GI helminth infections, and that these trade-offs make hosts less capable of mounting effective Th1-type immune responses against anthrax infections at this time. I also found evidence that coinfections and immune tradeoffs affect long-term host survival, and that GI parasites likely exert more selection pressure on zebra hosts than do ectoparasites and anthrax, but may actually be a stabilizing force in this host-pathogen system. Stress and reproductive hormones can modulate each other and the immune system, and can affect disease incidence. Pathogens can also cause host stress, as well as exploit host niches exposed by stress and reproductive hormone-induced immunomodulation. Therefore, I examined seasonal correlations between host stress, reproduction, and GI parasite coinfections in zebra and springbok in ENP. All three macroparasites examined (strongyle helminths, Strongyloides helminths, and Eimeria coccidia) had strongly seasonal signals, with hosts experiencing the highest parasite infection intensities during times of highest rainfall and highest anthrax outbreaks. Strongyles appeared to be perhaps most potent immunomodulating pathogen in this system, influencing zebra immune responses to anthrax and susceptibility to tick infestations, as well as springbok susceptibility to Strongyloides infections. However, helminths were mostly negatively associated with stress hormone concentrations and Eimeria had almost no interaction with stress, indicating that most hosts have developed tolerance toward even high macroparasite loads. Stress hormone concentrations were nearly uniformly higher in drier times than in wetter ones, and were positively affected by estrogen concentrations in females, likely indicating that seasonal nutritional and water stressors, as well as pregnancy stress during the dry season trumped the effects of pathogen infection intensities in causing host stress. In addition, adult animals had higher stress levels than did yearlings, despite yearlings being the largest aggregator of parasites, corroborating the idea that reproductive status is more influential in determining host stress than are pathogens in this system and that mechanisms of tolerance to GI parasites are substantial. In conclusion, my results indicate that GI parasites play a large role in determining host immune status and susceptibility to micro- and macroparasite coinfections. While ENP herbivores survive anthrax infections with regularity, host immunomodulation by GI parasites likely determines whether a host will mount a successful immune response against this potentially deadly pathogen. GI parasites modulate these coinfection interactions despite causing hosts little direct stress; thus, these coinfection interactions likely take place mostly through direct immunomodulatory effects rather than indirectly through host pathology, nutritional depletion, and other potentially stress-inducing sequelae. ENP zebra and springbok appear to be tolerant of their macroparasite loads, trading off parasite immunomodulatory and pathological effects in favor of balancing resource allocation toward reproductive efforts
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Visualizing Wildlife Conservation and Development in Southern Africa: A Multi-Optic Approach
Get PDFThe relationships between people and natural environments in coupled socio-ecological systems (SES) are complex. As complex adaptive systems with humans as one of the central drivers, coupled SES exhibit non-linear behavior, multiple stable-states, path dependence, and highly dynamic webs of connectivity across domains and scales. It should come as no surprise therefore that efforts to push these relationships towards greater sustainability are challenging to design and execute, particularly in resource constrained contexts with multiple competing actors. In this dissertation I examine conservation efforts in Zambia and Namibia from perspectives that vary along two gradients. Theoretically, my analyses are based upon epistemologies ranging from highly qualitative, interpretative and relational explanations of project outcomes, to highly quantitative models of spatially structured processes. Empirically, I draw upon ethnographic methods that seek to develop a grounds-eye view of reality, to satellite-sensed data which capture large scale patterns at the expense of context and detail. These two poles are bridged by an information framework that employs the meta-language of vision to describe and bound different forms of understanding, with an emphasis on rich articulations of context to enable dialogue across knowledges.Part I of the dissertation engages a long-standing debate about community-based natural resource management (CBNRM), which together with protected areas has been one the core conservation strategies across countries in southern Africa. Since the advent of CBNRM in the mid-1980s, scholars and practitioners have sought to explain the uneven performance of CBNRM programs. Most CBNRM assessments examine the underlying principles of community-based conservation, the local social and ecological contexts, and connections with larger political and historical patterns. I argue that analysis of the potential and pitfalls of CBNRM also requires an understanding of the institutional history and internal dynamics of projects that implement CBNRM reforms. Drawing upon theory and methods from development ethnography and public policy, I examine the rise and fall of CONASA, a second-generation CBNRM project in Zambia that operated in the early 2000s. CONASA was constituted from a merger of organizations and discourses to create continuity with previous projects. Its ambitious suite of activities included support for household livelihoods, community-based resource management, policy analysis, advocacy, and conservation enterprises at local, national, and transboundary levels. While individual activities were largely successful, CONASA's hybrid origins and logframe-centric management created fissures between its holistic design and daily operations, and hindered its ability to develop a broader narrative and maintain key alliances. This study illustrates the importance of understanding the interplay between project design and operational context in order to fully appreciate the possibilities and limitations of project-mode conservation.While a ground's eye view highlights context and nuances of process, the bird's eye view reveals pattern and emergent behavior across scales. In Part II, I present a new spatial modeling method for location data from orbiting satellites to analyze the spatiotemporal patterns in movement data. Advances in GPS technology have created both opportunities in ecology as well as a need for analytical tools that can deal with the growing volume of data and ancillary variables associated with each location. Time Local Convex Hull (T-LoCoH), is a home range construction algorithm that incorporates time into the construction and aggregation of local kernels. Time is integrated with Euclidean space using an adaptive scaling of the individual's characteristic velocity, enabling the construction of utilization distributions that capture temporal partitions of space as well as contours that differentiate internal space based on movement phase and time-use metrics. I test T-LoCoH against a simulated dataset and provide illustrative examples from a GPS dataset from springbok in Namibia. The incorporation of time into home range construction expands the concept of utilization distributions beyond the traditional density gradient to spatial models of movement and time, opening the door to new applications in movement ecology. Hulls also provide a means for characterization of the interactions between individuals, which are central to many aspects of population biology, including competition, predation, reproduction, resource optimization, and disease transmission. Classic measures of association are based on the intersection of static home range estimates and counts of matched locations, but the advances in GPS technology have created new possibilities for characterizing dynamic spatiotemporal properties of association. Hull metrics of association for both spatially and temporally overlapping hulls reveal the intensity of interaction both in raw terms as well as corrected for revisitation, as well as time lags. Similarly, a metric for the proportion of enclosed points constructed from the combined set of locations reveal the distribution of sharing across space and time for the entire time period. Illustrative examples of the methodology are provided using elephant tracking data from Tembe Elephant Park in South Africa. Plotting association metrics on a map, over time, and against other hull properties reveal novel patterns that can be basis for further study. Local hulls offer a promising approach for characterizing the spatiotemporal properties of association and exploring their covariates.Parts I and II of the dissertation both illustrate ways to pull out and characterize pattern in complex systems, but at scales and methods appropriate for the data and question. The challenge in seeing the 'whole picture' of complex coupled SES is not only to draw upon multiple disciplines and perspectives, but to do so in ways that enable dialog. Central to bridging nodes of knowledge is aggregation of detail into accessible and meaningful abstractions, embedding contextual information to inform new connections and enable extensions into new systems and domains, and making visible the spatial and social vantage points through which knowledge is produced and disseminated
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Exposure in motion: assessing disease risk through movement models and metrics
Get PDFExposure represents but one of several processes that underlie disease transmission dynamics in animal and human populations. Infection frequently depends on a number of complex interactions among factors related to the clinical properties of the pathogen (or the magnitude of the dose acquired upon contact) and the immune status of the host. When considering exposure, however, many of these aspects become trivial; the primary consideration is contact between a host and the infectious agent, whether it is harbored by another animal or an environmental reservoir. Contact, in turn, emerges from the space-use decisions of animals over time, potentially resulting in patterns that amplify or dilute the probability of encountering a pathogen. In this sense, the movement behavior of host animals is a fundamental determinant of disease dynamics. Using anthrax as its focal system, this dissertation aims to delve into the exposure process as it relates to the movement behaviors of host animals.A set of movement trajectories were collected via GPS collars fastened to zebra (Equus quagga) and springbok (Antidorcas marsupialis) in Etosha National Park in Namibia between 2009 and 2010. These data offer insight into the home ranging and habitat selection behaviors that characterize two ungulate species exhibiting susceptibility to anthrax infection and thus, form the basis of the analyses and models developed in this dissertation. Spatial overlap analysis represents one of the most common methods for evaluating the potential for disease exposure when movement data is available. In the case of an indirectly transmitted pathogen, such as Bacillus anthracis, the overlap between individuals may be less important than other characteristics of individual home range usage. Metrics such as revisitation (the rate at which an animal returns to a specific location) and duration rate (the length of time spent in a specific location) may be more informative, particularly if the locations of locally infectious zones (LIZs) are known. To assess the relative risk faced by zebra and springbok during the anthrax season, I developed a method that reduces the subjectivity in parameter selection when delineating home ranges using the Time Local Convex Hull (T-LoCoH) method. Using a cross-validation-based approach, the resulting site fidelity metrics are more directly comparable. The high values of the two site fidelity metrics imply that similar home ranging behavior among individuals can result in heterogeneous outcomes, contingent entirely upon the presence of a LIZ within an individual's home range.Much like spatial overlap analyses, habitat selection approaches can offer insight into patterns of potential risk with respect to exposure to disease, particularly in the case of environmentally-borne pathogens. When certain environmental characteristics can be associated with pathogen persistence, niche models can be developed and directly incorporated into the resource selection function framework. I used remotely sensed data on soil, bioclimatic, and vegetation covariates to build such a niche model for anthrax based on soil samples from 40 carcass sites in Etosha National Park harboring viable anthrax spores two or more years after deposition. When this risk layer was applied as a predictor in a step-selection function of zebra, a behaviorally-dependent pattern was evident. When animals were in the foraging state exhibited an avoidance of high risk areas, whereas the same animals were apparently attracted to those higher risk areas when moving in a directed manner. One possible explanation for this pattern is that zebra recognize not only where but also when they are most susceptible to anthrax, and adjust their behavior to reduce their risk.Another means of exploring the exposure process is through the use of simulation models. Due to the difficulty associated with comprehensive monitoring of susceptible host populations and infectious reservoirs, simulation models represent an ideal approach for extending general rules emerging from limited movement data to landscapes with known qualities. Using the behaviorally-contingent habitat selection framework created in Chapter 3, I explored the relationship between a set of environmental covariate layers and the exposure process whereby individuals encounter LIZs on the landscape. The method reveals that Wetness may represent a reasonable predictor of epidemic dynamics, with movement serving as the mediating process.The general analytical methods and models applied here serve to elucidate the role of individual movement behavior in the disease exposure process. Rather than analyzing data on case incidence or prevalence, these methods offer insight into the potential contact patterns that might give rise to endemic or epidemic infections. Thus, they reveal the manner by which analysis of host movements, particularly in conjunction with comprehensive (or simulated) data on the spatial distribution of infectious agents on a heterogeneous landscape, might aid in the management of transmission risk before any actual infections occur
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Everything Old Is New Again: Robust Predictive Frameworks for Shifting Host-Pathogen Interactions in the Face of Global Change
Get PDFDisease ecology urgently requires powerful predictive tools that anticipate the links between global change and emerging infectious disease. However, the ecological context of emerging disease remains poorly understood, especially given that the majority of parasites in any given ecosystem have no direct impact on human health. This dissertation explores a global change biology approach to host-pathogen interactions, focused on understanding both positive and negative impacts of climate change on parasites and pathogens. Chapter 1 reviews current theory surrounding extinction, including mathematical modeling approaches at scales from population extirpation up through global extinction rates. Community-level approaches to extinction risk estimation are applied in Chapter 2, which includes forecasts for climate-driven range shifts based on the largest macroparasite occurrence dataset yet assembled. Up to a third of parasites could face extinction in a changing climate, especially accounting for co-extinction with hosts. However, we find no evidence that wildlife parasites face better or worse odds of survival (or have different hotspots of diversity) based on their potential to infect humans. The results of this study indicate the hundreds of thousands, or potentially millions, of parasitic species on Earth are likely to be redistributed around the globe in a hard to predict pattern, with unknown effects on wildlife and human health. The same species distribution modeling methods from Chapter 2 are used in Chapter 3 to predict the global distribution of Zika virus, an emerging infection from 2016 with a still largely unresolved eco-epidemiology. The conflict among different models and modeling approaches surrounding Zika's distribution is considered in Chapter 4, by interfacing these models with simulations of potential epidemics in the United States. Overall, this dissertation addresses the idea that in the face of global change, ecologists will play an increasingly important role in predicting shifting landscapes of disease. However, the overwhelming focus on emergence ignores the importance of extinction as a potentially complementary phenomenon within ecosystems; and the varied approaches within ecology, and the short timescale on which ecologists work during current outbreaks, pose a disciplinary problem with no clear answer
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Wildlife Sustainability and Human Food Security in Cameroon, Central Africa
Get PDFConcerns about the sustainability of wildlife hunting, particularly in Central Africa, have dominated the scientific literature on wildlife utilization. Only more recently have researchers began considering the human dependence on wildlife for both nutritional needs as well as sources of livelihoods. I begin with a systematic literature review of the wildlife harvesting literature, examining in detail the type of sustainability indicators predominating in the literature and their strengths and weaknesses. We find that indicator type, continent of study, species body mass, taxonomic group, and socioeconomic status of study site are important predictors of the probability of reported sustainability. Indicators relying on population-specific biological data are most often used in North America and Europe, while cruder estimates are more often used in Africa, Latin America, and Oceania. Our results highlight both the uncertainty and lack of uniformity in sustainability science. This presents a major gap in our ability to monitor wildlife and its use, since the importance of wildlife for human consumption is at its greatest precisely in the places where indicators used are the weakest. We point to future directions in the field.Subsequent field work was conducted in the humid forest zone of southeastern Cameroon in Central Africa. Cameroon is one of the six Congo Basin countries, and there has traditionally been great concern on the part of environmental conservation organizations over the level of wildlife hunting in the country. The first part of my field work was a pilot study to compare field methodologies for wildlife consumption by rural peoples. For wildlife surveys, I used distance sampling on wildlife transects to determine presence/absence and abundance of wildlife species in four different village sites that represent a gradient of human impact and environmental intactness. To evaluate human use of wildlife relative to economic status, I used household surveys with heads of households to ascertain relative wealth status and other household demographic and economic parameters as they relate to wildlife use and consumption. Finally, I tested methodologies for enumerating hunter activity and catch-per-unit-effort (CPUE) as a potentially useful tool for monitoring the status of hunting sustainability. Results indicate that transect surveys do in fact detect increasing wildlife species in more rural, intact village sites, although sample sizes were too small to enumerate actual wildlife densities. Further, more rural households tend to both hunt and consume more wildlife; wildlife use in rural areas thus forms a more important source of total livelihood than for more urban households. Although humans have hunted wildlife for millennia, and it remains an important source of animal protein, there is increasing concern that `bushmeat' hunting, particularly in central Africa, is unsustainable. We explore the role that wildlife and alternative meat sources play in the food security of human populations in southeastern Cameroon. We conducted a large, cross-sectional study in 24 village and town sites in southeastern Cameroon to evaluate the role of wildlife in human food security in a gradient from urban to rural households. Rural households are significantly more likely to rely on wildlife for animal protein, whereas urban households rely on significantly more domestic meat. Using generalized linear mixed modeling, we found significant associations between bushmeat hunting and consumption and positive effects on food security, highlighting the importance of wildlife to human security in the Congo Basin. We asked interviewees about most consumed and most preferred wildlife species; interestingly, there is a potential synergy between taste preferences and the more resilient species that are hunted.These results indicate that wildlife consumption plays an important role in human food security in the humid forest zone of southeastern Cameroon. Disappearance of wildlife would negatively impact the food security situation in the region, particularly in the forms of protein-energy malnutrition and iron deficiency. At present, there is little ability to maintain small animal husbandry due to the poor veterinary services throughout the region. I evaluate the cost-effectiveness of a `Heifer International' model extended to two of the ten provinces in Cameroon that make up the region where wildlife hunting is currently the most important form of animal protein, consisting of the Southern and Eastern provinces ("Regions"), which together have a population of about 1 million people. The Heifer International model would replace the animal protein traditionally taken from wildlife sources with a revolving "micro-loan" of livestock, that must be eventually passed on to neighbors. At a population density of around 8 people/km2, wildlife hunting is believed to be at least four times above maximum sustainable wildlife hunting rates, and therefore supplementary forms of animal protein need to come from elsewhere. Assuming administrative and training costs are included in the prices of the animals as estimated, a `Heifer International' model of small animal husbandry would be a cost-effective way to address protein-energy malnutrition and iron deficiency, as well as wildlife conservation concerns in this part of the world
Contact with domestic dogs increases pathogen exposure in endangered African wild dogs (Lycaon pictus).
Get PDFBACKGROUND:Infectious diseases have contributed to the decline and local extinction of several wildlife species, including African wild dogs (Lycaon pictus). Mitigating such disease threats is challenging, partly because uncertainty about disease dynamics makes it difficult to identify the best management approaches. Serious impacts on susceptible populations most frequently occur when generalist pathogens are maintained within populations of abundant (often domestic) "reservoir" hosts, and spill over into less abundant host species. If this is the case, disease control directed at the reservoir host might be most appropriate. However, pathogen transmission within threatened host populations may also be important, and may not be controllable by managing another host species. METHODOLOGY/PRINCIPAL FINDINGS:We investigated interspecific and intraspecific transmission routes, by comparing African wild dogs' exposure to six canine pathogens with behavioural measures of their opportunities for contact with domestic dogs and with other wild dogs. Domestic dog contact was associated with exposure to canine parvovirus, Ehrlichia canis, Neospora caninum and perhaps rabies virus, but not with exposure to canine distemper virus or canine coronavirus. Contact with other wild dogs appeared not to increase the risk of exposure to any of the pathogens. CONCLUSIONS/SIGNIFICANCE:These findings, combined with other data, suggest that management directed at domestic dogs might help to protect wild dog populations from rabies virus, but not from canine distemper virus. However, further analyses are needed to determine the management approaches--including no intervention--which are most appropriate for each pathogen
Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore.
Get PDFAnticoagulant rodenticide (AR) poisoning has emerged as a significant concern for conservation and management of non-target wildlife. The purpose for these toxicants is to suppress pest populations in agricultural or urban settings. The potential of direct and indirect exposures and illicit use of ARs on public and community forest lands have recently raised concern for fishers (Martes pennanti), a candidate for listing under the federal Endangered Species Act in the Pacific states. In an investigation of threats to fisher population persistence in the two isolated California populations, we investigate the magnitude of this previously undocumented threat to fishers, we tested 58 carcasses for the presence and quantification of ARs, conducted spatial analysis of exposed fishers in an effort to identify potential point sources of AR, and identified fishers that died directly due to AR poisoning. We found 46 of 58 (79%) fishers exposed to an AR with 96% of those individuals having been exposed to one or more second-generation AR compounds. No spatial clustering of AR exposure was detected and the spatial distribution of exposure suggests that AR contamination is widespread within the fisher's range in California, which encompasses mostly public forest and park lands Additionally, we diagnosed four fisher deaths, including a lactating female, that were directly attributed to AR toxicosis and documented the first neonatal or milk transfer of an AR to an altricial fisher kit. These ARs, which some are acutely toxic, pose both a direct mortality or fitness risk to fishers, and a significant indirect risk to these isolated populations. Future research should be directed towards investigating risks to prey populations fishers are dependent on, exposure in other rare forest carnivores, and potential AR point sources such as illegal marijuana cultivation in the range of fishers on California public lands
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Applications of Data-driven Modeling to Infectious Diseases in Africa: Anthrax in Wildlife and HIV in Humans
Get PDFThe goal of epidemiology is to identify the biological, behavioral, and environmental causes of health outcomes or diseases and apply this knowledge to the development of effective disease interventions. Diseases are complex phenomena that arise from various interacting processes, challenging epidemiologists and disease ecologists to extract important causal relationships from observational and experimental data. While data from properly designed experimental studies are the gold standard for assessing the existence of a causal relationship, such studies may be logistically or morally infeasible in many situations. Observational data has the advantage of generally being less invasive, cheaper, and more readily available. However, such data are often plagued by a variety of biases, challenging our understanding of the underlying dynamical processes. However, by explicitly modeling the observation and sampling processes in addition to the underlying biological and behavioral processes of interest it is often possible to understand the latter more rigorously. In this dissertation, I develop empirical and analytical methods to understand the dynamics of rabies virus, canine distemper virus, Bacillus anthracis, and the human immunodeficiency virus using observational surveillance data. Importantly, models are built from the data up with the focus being on what is known about the system from the data rather than other mechanistic processes for which we know little
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